1. Field of the Invention
The present invention relates to a white balance adjustment apparatus for use in a digital camera, a video camera, etc., and relates to a white balance coefficient calculation method for use in white balance correction.
2. Description of the Related Art
Generally, a digital camera or a video camera is provided with an auto white balance adjustment apparatus for automatically correcting color balance so as to the color of a white color light source becomes achromatic. Thereby, a photograph with a color tone having no feeling of wrongness can be obtained by producing satisfactory results of chromatic adaptation in a human visual system on a finished photograph in a pseudo manner. To perform the white balance correction, it is firstly necessary to measure a white color itself. Conventionally, a method for measuring a white color by using an output from a photometrical sensor provided separately from an imager element of a camera, or a method for detecting a white color on the basis of image data from an imager element has been adopted. Since the method for measuring the white color by using the output from the photometrical sensor increases a cost and an image acquisition range and a photometrical range are not always agree with each other, errors are unavoidable. Therefore, generally, a method for detecting the color of the light source (achromatic color) on the basis of the image data from the imager element has been mainly adopted.
However, in such a method for detecting the color of the light source based on the image data, in the case where there is no or very few color of the light source (achromatic color) in the image data, the method suffers from the disadvantage that a precise white balance correction cannot be performed. As regards such a problem, a method for performing white balance control by using images of a plurality of frames including image data which has acquired previously is disclosed in U.S. Pat. No. 6,160,579 and Jpn. Pat. Appln. KOKAI Publication No. 5-83729. According to this method, even if no color of the light source exists in the image to be applied the white balance control, a detection probability of the light source color can be increased by using images of other frames.